APP_STL := c++_shared
ndk-build only allows you to select one runtime for your app, and can only do in
Application.mk.
Use clang directly
If you're using clang directly in your own build system, clang++ will use
c++_shared by default. To use the static variant, add -static-libstdc++ to
your linker flags. Note that although the option uses the name "libstdc++" for
historical reasons, this is correct for libc++ as well.
Important considerations
Static runtimes
If all of your application's native code is contained in a single shared
library, we recommend using the static runtime. This allows the linker to
inline and prune as much unused code as possible, leading to the most optimized
and smallest application possible. It also avoids PackageManager and dynamic
linker bugs in old versions of Android that make handling multiple shared
libraries difficult and error-prone.
That said, in C++, it is not safe to define more than one copy of the same
function or object in a single program. This is one aspect of the
One Definition Rule present in the C++ standard.
When using a static runtime (and static libraries in general), it is easy to
accidentally break this rule. For example, the following application breaks this
rule:
# Application.mk
APP_STL := c++_static
# Android.mk
include $(CLEAR_VARS)
LOCAL_MODULE := foo
LOCAL_SRC_FILES := foo.cpp
include $(BUILD_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := bar
LOCAL_SRC_FILES := bar.cpp
LOCAL_SHARED_LIBRARIES := foo
include $(BUILD_SHARED_LIBRARY)
In this situation, the STL, including and global data and static constructors,
will be present in both libraries. The runtime behavior of this application is
undefined, and in practice crashes are very common. Other possible issues
include:
Memory allocated in one library, and freed in the other, causing memory
leakage or heap corruption.
Exceptions raised in libfoo.so going uncaught in libbar.so, causing your
app to crash.
Buffering of std::cout not working properly.
Beyond the behavioral issues involved, linking the static runtime into multiple
libraries will duplicate the code in each shared library, increasing the size of
your application.
In general, you can only use a static variant of the C++ runtime if you have one
and only one shared library in your application.

Shared runtimes

If your application includes multiple shared libraries, you should use
libc++_shared.so.
On Android, the libc++ used by the NDK is not the same as the one that's part
of the OS. This gives NDK users access to the latest libc++ features and bug
fixes even when targeting old versions of Android. The trade-off is that if you
use libc++_shared.so, you must include it in your app. If you're building your
application with Gradle this is handled automatically.
Old versions of Android had bugs in PackageManager and the dynamic linker
that caused installation, update, and loading of native libraries to be
unreliable. In particular, if your app targets a version of Android earlier
than Android 4.3 (Android API level 18), and you use libc++_shared.so, you
must load the shared library before any other library that depends on it.
The ReLinker project offers
workarounds for all known native library loading problems, and is usually
a better choice than writing your own workarounds.
One STL per app
Historically the NDK supported GNU libstdc++ and STLport in addition to libc++.
If your application depends on prebuilt libraries that were built against an NDK
different than the one used to build your application, you will need to ensure
that it does so in a compatible manner.
An application should not use more than one C++ runtime. The various STLs are
not compatible with one another. As an example, the layout of std::string
in libc++ is not the same as it is in gnustl. Code written against one STL will
not be able to use objects written against another. This is just one example;
the incompatibilities are numerous.

This rule extends beyond your code. All of your dependencies must use the same
STL that you have selected. If you depend on a closed source third-party
dependency that uses the STL and does not provide a library per STL, you do not
have a choice in STL. You must use the same STL as your dependency.
It is possible that you will depend on two mutually incompatible libraries. In
this situation the only solutions are to drop one of the dependencies or ask the
maintainer to provide a library built against the other STL.

C++ Exceptions
C++ exceptions are supported by libc++, but they are disabled by default in
ndk-build. This is because historically C++ exceptions were not available in the
NDK. CMake and standalone toolchains have C++ exceptions enabled by default.
To enable exceptions across your whole application in ndk-build, add the
following line to your Application.mk file:
APP_CPPFLAGS := -fexceptions
To enable exceptions for a single ndk-build module, add the following line to
the given module in its Android.mk:
LOCAL_CPP_FEATURES := exceptions
Alternatively, you can use:
LOCAL_CPPFLAGS := -fexceptions
As with exceptions, RTTI is supported by libc++, but is disabled by default in
ndk-build. CMake and standalone toolchains have RTTI enabled by default.
To enable RTTI across your whole application in ndk-build, add the following
line to your Application.mk file:
APP_CPPFLAGS := -frtti
To enable RTTI for a single ndk-build module, add the following line to the
given module in its Android.mk:
LOCAL_CPP_FEATURES := rtti
Alternatively, you can use:
LOCAL_CPPFLAGS := -frtti
  
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
  
Last updated 2024-01-03 UTC.
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